The present invention relates to a fluorescent tube assembly and particularly one which is portable and can be manually moved about and suspended at a work site to aid a user in obtaining the best lighting conditions. It has been the practice to use incandescent light bulbs, suitably encased in light guards, for this purpose. Such lights are often referred to as trouble lamps, extension lights, work lights, inspection lights, and the like, and are commonly employed by mechanics and other workers who require a concentration of light in a frequently changing location.
Fluorescent lights have several advantages over incandescent bulbs. As an example, for the same wattage, fluorescent lights usually provide more light with less glare. U.S. Pat. No. 3,953,761 to Lo Giudice reports that a fluorescent light tube consumes approximately one-sixth of the energy or electrical current required by an incandescent bulb to produce the same amount of light output. Thus, particularly in the present time of energy crisis, substantial energy savings can be effected by the use of fluorescent light tubes instead of incandescent bulbs. Moreover, the same patent mentions that fluorescent light tubes have a life expectancy which is up to 10 times longer than that of conventional incandescent light bulbs.
While it has been suggested to provide extension lights using the usual incandescent bulbs at normally supplied voltages, such as 110 volts to 120 volts, with an electrical outlet, as illustrated in U.S. Pat. No. 2,653,219 to Popp, this has not occurred to applicant's knowledge with fluorescent tube assemblies and especially with those designed for portable use. One reason for this disparity is that fluorescent tubes require different circuitry supplying higher voltages than voltages normally supplied at wall outlets and the like.
Fluorescent tubes or lamps ordinarily comprise an elongated glass bulb having mercury vapor, sodium vapor, or still other gases which produce ultraviolet light when electrically excited. This light may also cause phosphors, if present on the inside of the tube, to luminesce. The tube has terminals at each end, usually in the form of a pair of protruding pins.
To start or fire a fluorescent tube, a higher voltage is required than that needed to maintain the tube in a lighted condition once the initial higher voltage barrier is overcome. For this purpose, a fluorescent tube has electric starter means within each end of the tube, often in the form of fine tungsten filaments. To fire the tube, the starting filaments may be heated by a relatively high voltage until an arc or discharge is struck between the two heated filaments. This requires a flow of high voltage current through the filaments before the arc or discharge is struck and the lamp begins its illumination, or until the gas in the tube ionizes to conduct a current through the tube. Thereafter, a relatively low voltage may be used to maintain the tube in a lighted condition.
A ballast, sometimes referred to as a coil or choke coil, is commonly used in a circuit for a fluorescent tube to obtain the higher voltage needed to fire it. The ballast is essentially a transformer. The presence of such relatively high voltage in a unit has made it hazardous to operating personnel to incorporate in the tube assembly still other electric features such as convenience outlets. The higher voltage present can increase the likelihood of electric short circuits to other parts of the circuit such as to electric outlets. This has discouraged the adaptability of fluorescent tube assemblies and especially the portability of such assemblies where the presence of additional convenience outlets would be most useful.